1. Field of the Invention
The present invention relates to techniques for routing a UBR (Unspecified Bit Rate) connection in an ATM (Asynchronous Transfer Mode) network.
2. Description of the Related Art
In recent years, the development of ATM networks has been promoted, and the principal purpose thereof consists in expediting existing LANs (Local Area Networks). In this regard, LAN data are transmitted through UBR connections within the ATM network in most cases. It is therefore conjectured that messages based on UBR connections will form a great majority of the traffic on an ATM network.
Accordingly, how to efficiently set the UBR connections becomes important when improving effective load distribution and utilization of resources, etc. in the ATM network.
The features of the UBR connection are as listed below:
(1) The UBR connection has the lowest quality among the four service categories of a CBR (Continuous Bit Rate) connection, a VBR (Variable Bit Rate) connection, an ABR (Available Bit Rate) connection and the UBR connection.
(2) The network does not guarantee a bandwidth requested by the user thereof.
(3) A request for a transmission quality is not be made by the user.
(4) On account of the above property (2), the network does not administer the bandwidths of the UBR connections.
In general, in determining a route for a connection, an ATM exchange checks the physical conditions (such as the occurrence of any fault) of communication lines including the route therein, it acquires a requested bandwidth on the route, it reserves connection resources on the route, and it secures a requested quality on the route. As indicated in FIG. 1, however, it is the actual situation of a UBR connection that only two factors; the check of the physical conditions of the lines including the UBR connection route therein, and the reservation of the connection resources on the route, are used for the determination of the route on account of the properties (1)-(4) of the UBR connection mentioned above.
For this reason, such UBR connections might be concentrated on a single route insofar as the physical conditions of the lines including the route therein are normal and as the connection resources on the route are still in surplus (that is, as the number of connections set on the route is smaller than the upper limit of connections).
Accordingly, the present-day system for routing a UBR connection has the problem that effective load distribution and utilization of resources cannot be improved in an ATM network.